Introduction to the use of CMD command line pipeline command


1、 What are pipeline commands

The pipeline command can filter the execution result of a command and keep only the information we need.
If the dir command will display all the folders and files in the directory, you can use the pipeline command | findstr “” to filter the results of dir and keep only the information needed

|Command pipeline

Format: first order | second order [| third order…]
Use the result of the first command as an argument to the second command. Remember that this is common in UNIX.

For example:

dir c:\|find “txt”

The above command is: find all C: \, and find the txt string.

Please check the function of find by yourself with find /

This is how I automatically format a disk when I don’t make format’s auto format parameters
echo y|format a: /s /q /v:system
All of you who have used format know that you need to enter y to confirm whether it is a grid. This command is preceded by echo y and uses the character |
Is passed to the format command
So as to achieve the purpose of inputting y automatically
(this command is dangerous, please be careful when testing)

The most commonly used output y to the following statement

echo y|delete *.txt /s

2、 Use of pipe command

1. Windows netstat view port and process usage

//If we need to determine who's using our port 9050

C:/>netstat -aon|findstr "9050"
//See? The port is occupied by a process with process number 2016. Continue to execute the following command:
C:/>tasklist|findstr "2016"
tor.exe 2016 Console 0 16,064 K
//It's clear, tor.exe  It's taking up your port

2. View folder directory structure

tree > list.txt

tree /f >list.txt

3. I / O redirection

Echo – C / / – C: does not wrap, Linux is – n

I / O redirection:
For each naming, there are three related files. Standard input file, standard output file, error output file
Because under UNIX / Linux, any device is treated as a file. In fact, all standard input files are keyboards,
Standard output and error output files are screens
>Output redirection
< input redirection
< < input append
>>Input append
File descriptor:
Each file can be described by a file descriptor. The system provides 12, and 3-9 can be defined arbitrarily. 0-2 system definition is as follows:
0 standard input keyboard
1. Standard output display
2. Error output display
That is, 0-2 can be used to represent the above three files
For example, the output of CMD > file / / CMD is redirected to the file file
The output of CMD > > file / / CMD is appended to the file, otherwise it is created
CMD 1 > file / / redirect the standard output of the shell running CMD to file, and 1 represents the standard output
CMD > file 2 > & 1 / / redirect the output of CMD to file and 2 (error output) to 1 (standard output)
If 2 > 1, 1 will be regarded as a file, and it is necessary to use & 1 to direct errors to 1
CMD 2 > file / / direct the error output to file
CMD > > file 2 > & 1 / / append error and CMD output to file, CMD > > file, append; 2 > & 1, error directed to
Standard output and standard input are appended to the file, so both error and CMD output are appended to the file
CMD 1 > > file 2 > & 1 / / this command can be equivalent to the previous command
The input of cmdfile2 / / CMD is file1, and the result is output to File2
CMD < < end / / CMD uses standard input until end is encountered. End can be any character
Understanding: CMD uses the default standard input, run, when encountering end, it will be appended, but the standard input and output
Unable to append, so error exit
Note: according to the statement in Chapter 25 of Linux shell programming,
This is the syntax defined by the shell. It can be directly interpreted as end as the separator
CMD < & M / / take the file descriptor m as the input of CMD
CMD > & M / / take the file descriptor m as the output of CMD
CMD < & – / / turn off standard input
!! Note:
1. Do not add a space before the input and output directional character, otherwise unexpected problems may occur
2. 0 1 2 cannot use > > or < < directional character, for example: 2 > > & 1 error

Use the pipe character to enter Y / N automatically

Sometimes, when calling the CMD command, the prompt message will appear. For example, when using PSCP, the prompt message will appear as follows:
Store key in cache?(y/n)
You need to enter y or n every time. If you call the CMD command in Java or python, you will not be able to execute it. What can I do? You can use the pipe symbol to do this, such as the command PSCP. You can fill in Y automatically by using the following method:

echo y |pscp ……

The ellipsis at the end is the operation command;
Other language calls can also run normally

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